1. Field of the Invention
This invention relates to a semiconductor device composed of a transistor for modulation and a semiconductor laser as one body and a process for the production of the same.
2. Description of the Prior Art
Semiconductor optical circuit elements, for example, light-emitting devices such as light-emitting diodes and semiconductor lasers, optical modulation elements, and light-detecting devices such as avalanche photodiodes and the like, and semiconductor electronic circuit elements, for example, transistors, diodes and the like, should have different epitaxial structures. When these two kinds of circuit elements can be formed on the same substrate, it is possible to realize miniaturization of the device, improved high frequency characteristics and reliability and lower production cost. Thus, a useful technique has strongly been desired for the purpose of forming these two kinds of circuit elements on the same substrate.
Various reports have hitherto been made on a method of forming a semiconductor laser and transistor for the modulation of this laser on the same substrate. In these methods, an epitaxial wafer having both an epitaxial multilayer for a laser and an epitaxial layer for a field-effect transistor is used. That is, in the wafer surface, there is formed the epitaxial layer in a zone for the field-effect transistor and the epitaxial multilayer in a zone for the laser by partially etching the wafer surface or by the use of diffusion, and these elements are connected by a semiconductor layer or metal. However, a very complicated process is required for the fabrication of these elements, and not much electric current can flow because of the use of a field-effect transistor of Shottky-barrier gate type using an n-type semiconductor layer on a semi-insulating substrate as an active layer. As to semiconductor lasers, various stripe structures to obtain a fundamental mode in the lateral direction have been reported, but each of these structures is too complicated.